Porous cube-aggregated Co₃O₄ microsphere-supported gold nanoparticles for oxidation of carbon monoxide and toluene

Porous cube-aggregated monodisperse Co₃O₄ microspheres and their supported gold (xAu/Co₃O₄ microsphere, x=1.6-7.4 wt %) nanoparticles (NPs) were fabricated using the glycerol-assisted solvothermal and polyvinyl alcohol-protected reduction methods. Physicochemical properties of the materials were characterized by means of numerous analytical techniques, and their catalytic activities were evaluated for the oxidation of toluene and CO. It is shown that the cubic Co₃O₄ microspheres were composed of aggregated cubes with a porous structure. The gold NPs with a size of 3.2-3.9 nm were uniformly deposited on the surface of Co₃O₄ microspheres. Among the Co₃O₄ microsphere and xAu/Co₃O₄ microsphere samples, the 7.4Au/Co₃O₄ microspheres performed the best, giving T_{90 %} values (the temperature required for achieving a CO or toluene conversion of 90 % at a weight hourly space velocity of 20 000 mL g^-1 h^-1) of -8 and 250 °C for CO and toluene oxidation, respectively. In the case of 3.0 vol % water vapor introduction, a positive effect on CO oxidation and a small negative effect on toluene oxidation were observed over the 7.4Au/Co₃O₄ microsphere sample. The apparent activation energies obtained over the xAu/Co₃O₄ microsphere samples were in the ranges of 40.7-53.6 kJ mol^-1 for toluene oxidation and 21.6-34.6 kJ mol ^-1 for CO oxidation. It is concluded that the higher oxygen adspecies concentration, better low-temperature reducibility, and stronger interaction between gold NPs and Co₃O₄ as well as the porous microspherical structure were responsible for the excellent catalytic performance of 7.4Au/Co₃O₄ microsphere. In the world of microspheres and cubes: Porous Co₃O₄ monodisperse microspheres and xAu/Co₃O₄ microsphere (x=1.6-7.4 wt %) are prepared using glycerol-assisted solvothermal and polyvinyl alcohol-protected reduction methods, respectively. The higher oxygen adspecies concentration, better low-temperature reducibility, and strong interaction between gold and Co₃O₄ are responsible for the excellent catalytic performance of 7.4Au/Co₃O₄ microspheres.